<meta charset="utf-8">
(#) Implements custom TLS trust manager

!!! WARNING: Implements custom TLS trust manager
   This is a warning.

Id
:   `CustomX509TrustManager`
Summary
:   Implements custom TLS trust manager
Severity
:   Warning
Category
:   Security
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   7.0.0 (July 2021)
Affects
:   Kotlin and Java files and library bytecode
Editing
:   This check runs on the fly in the IDE editor
See
:   https://goo.gle/CustomX509TrustManager
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/X509TrustManagerDetector.java)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/X509TrustManagerDetectorTest.kt)

This check looks for custom `X509TrustManager` implementations.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/test/pkg/InsecureTLSIntentService.java:15:Warning: Implementing a
custom X509TrustManager is error-prone and likely to be insecure. It is
likely to disable certificate validation altogether, and is non-trivial
to implement correctly without calling Android's default implementation.
[CustomX509TrustManager]
    TrustManager[] trustAllCerts = new TrustManager[]{ new X509TrustManager() {
                                                           ----------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`src/test/pkg/InsecureTLSIntentService.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
package test.pkg;

import android.app.IntentService;
import android.content.Intent;

import java.security.GeneralSecurityException;
import java.security.cert.CertificateException;

import javax.net.ssl.HttpsURLConnection;
import javax.net.ssl.SSLContext;
import javax.net.ssl.TrustManager;
import javax.net.ssl.X509TrustManager;

public class InsecureTLSIntentService extends IntentService {
    TrustManager[] trustAllCerts = new TrustManager[]{ new X509TrustManager() {
        @Override
        public java.security.cert.X509Certificate[] getAcceptedIssuers() {
            return null;
        }

        @Override
        public void checkClientTrusted(java.security.cert.X509Certificate[] certs, String authType) {
        }

        @Override
        public void checkServerTrusted(java.security.cert.X509Certificate[] certs, String authType) throws CertificateException {
        }
    }};

    public InsecureTLSIntentService() {
        super("InsecureTLSIntentService");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        try {
            SSLContext sc = SSLContext.getInstance("TLSv1.2");
            sc.init(null, trustAllCerts, new java.security.SecureRandom());
            HttpsURLConnection.setDefaultSSLSocketFactory(sc.getSocketFactory());
        } catch (GeneralSecurityException e) {
            System.out.println(e.getStackTrace());
        }
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/X509TrustManagerDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `X509TrustManagerDetector.testTrustsAll`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("CustomX509TrustManager")
  fun method() {
     problematicStatement()
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("CustomX509TrustManager")
  void method() {
     problematicStatement();
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection CustomX509TrustManager
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="CustomX509TrustManager" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'CustomX509TrustManager'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore CustomX509TrustManager ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

<!-- Markdeep: --><style class="fallback">body{visibility:hidden;white-space:pre;font-family:monospace}</style><script src="markdeep.min.js" charset="utf-8"></script><script src="https://morgan3d.github.io/markdeep/latest/markdeep.min.js" charset="utf-8"></script><script>window.alreadyProcessedMarkdeep||(document.body.style.visibility="visible")</script>